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Progressive Rinse: A new Approach at Reducing Waste from Indoor Residual Spray Campaigns

  1. Rwanda: Mosquito Nets Used for Fishing
  2. Progressive Rinse: A new Approach at Reducing Waste from Indoor Residual Spray Campaigns

Rwanda: Mosquito Nets Used for Fishing
The New Times (Kigali, Rwanda)
February 22, 2007 Musanze.

The malaria campaign in Gacaca Sector was last year affected by residents' involvement in the sale of the mosquito nets and also using them for fishing activities.

While talking to this reporter last Friday, a sector official who requested anonymity said the mosquito nets meant for malaria control were instead used for catching small fish in Ruhondo River by some residents. He pointed out that the problem was brought about due to lack of sensitization campaigns by the local leaders and ministry officials. He however said authorities arrested some residents for misusing the nets as a deterrent measure but later released them.

Progressive Rinse: A new Approach at Reducing Waste from Indoor Residual Spray Campaigns
By: Manuel F. LLuberas MS, IDHA, Vector Control Systems Manager, HD Hudson Manufacturing Company;
Paul Banda Dip PHI, Dip M&F, Manager Malaria Control Programme, Konkola Copper Mines plc, Zambia.

Malaria continues to pose a health risk for approximately 50% of the world's population, most of which lives in the world's poorest countries. Though the disease was once widespread, active vector control successfully eliminated it from many countries in temperate climates during the mid 20th Century. Today, malaria is very commonly found throughout the tropical and sub-tropical regions of the world, causing more than 300 million acute illnesses and at least one million deaths annually. In sub-Saharan Africa, one child dies every 30 seconds. In light of this, many countries have opted to implement indoor residual spraying (IRS) campaigns as part of an integrated vector management (IVM) program to keep vector populations under control and fight against the spread of the disease. Unfortunately, though indoor residual spraying is extensively used and has demonstrated effective in many areas, especially for malaria and Chagas vector control, vector control programs frequently lack well trained field staff familiar with the series of requirements, expectations and limitations associated with the use of insecticides. This is especially patent and troublesome in many of the programs that had been inactive for decades and are considering including DDT in their vector control arsenal.

The objective of vector control programs is the reduction of malaria morbidity and mortality by reducing vector populations and thus disease transmission. Implementing a vector control program depends on the magnitude of the malaria burden, the feasibility of timely and correct application of the required interventions and the possibility of sustaining the resulting modified epidemiological situation. A systematic approach to vector control based on evidence and knowledge of the local situation is the only way to ensure the program’s objectives are met. In the wake of the Stockholm Convention on Persistent Organic Pollutants, previous recommendations provided in WHO’s Manual for Indoor Residual Spraying: Application of Residual Sprays for Vector Control would have to be modified; especially in programs using DDT. The recommendation in section 8 of the manual titled Disposal of remains of insecticides and empty packaging states:

At the end of the day's work, put the washings from the sprayer into pit latrines, if available, or into pits dug especially for this purpose and away from sources of drinking water. Dilute any insecticide with more water before putting into pits.

Disposing of excess material in this fashion is troublesome, but disposal of DDT following this recommendation is a clear violation of the POPs Convention.

In light of this, excess material and rinse water would have to be carefully contained and disposed of according to Convention guidelines. Under current guidelines, DDT and DDD are potential candidates for incineration in a rotary kiln at 820–1,600 ?C. Disposal of DDT formulated in 5% oil solution or other solutions is mainly by using liquid injection incineration at 878–1,260 deg C, with a residence time of 0.16–1.30 seconds and 26–70% excess air. Destruction efficiency with this method is reported to be >99.99%. Multiple-chamber incineration is also used for 10% DDT dust and 90% inert ingredients at a temperature range of 930–1,210 ?C, a residence time of 1.2–2.5 seconds, and 58–164% excess air. DDT powder may be disposed of by molten salt combustion at 900 ?C (no residence time or excess air conditions specified). A low temperature destruction method involving milling DDT with Mg, Ca, or CaO is under development on a laboratory scale, but this method is not currently available. Unfortunately, there are very few adequate incinerators in the world, and almost all of them are located in developed countries. Regrettably, the strict requirements for proper disposal by incineration at very high temperatures create an enormous burden for a developing country, both economically and technologically. Moreover, legal aspects concerning trans-border movement of toxic chemicals make the problem of safe disposal more complicated and costly. It should be considered, on a case-by-case basis, whether perpetual storage of unwanted POPs awaiting proper incineration would be a safer alternative than a feasible, but not entirely appropriate disposal (e.g. burying below topsoil).

A simpler, more practical solution to this problem would be to recycle the water resulting from rinsing the compression sprayers at the end of each spray day. This water could then be used to partially fill the initial charge of the sprayer the following day of operation. The process is elegantly simple and would dramatically reduce, if not completely eliminate environmental contamination.

The progressive rinse method involves setting up a rinse station where seven to nine plastic containers of 200-liter capacity (50 gallons) at a central location where IRS activities are coordinated. The first container is kept empty while half of the remaining containers are filled with clean water and the other half are empty.

At the end of the spray day, spray teams return to their staging areas, the sprayers are depressurized and left-over insecticide in them is poured in the first container (No. 1; empty). They then add one to two liters to the sprayer from the second container (No. 2; filled with clean water). The sprayer is then closed and pressurized to approximately 25 psi (2 bar), shaken so all inside surfaces are rinsed and the contents sprayed into the third container (No. 3; empty). Once the sprayer is empty, it is depressurized and the remaining contents are poured into the container (No. 3; empty). The sprayman then repeats the process at the next two stages –containers No. 4 (full) & 5 (empty) and container No. 6 (full) & 7 (empty). Upon completing of three stages, the sprayers have gone through a triple rinse procedure that should produce clean rinse water. At this point, the sprayers are considered cleaned.

The rinse water generated in this fashion is kept in the rinse containers. The next day, about one to two liters of the rinse water is poured in each sprayer. Once at the target area, each sprayer can be filled to its capacity with clean water.

The process continues on a daily basis until the spray season ends. At this point, the rinse water can be decontaminated following appropriate methods or kept in a secure location until the beginning of the next spray cycle. Implementing progressive rinse procedures as part of the routine operations of an indoor residual spray campaign will eliminate environmental contamination resulting from cleaning compression sprayers following WHO recommendations and help maintain sprayers in optimal conditions while meeting the requirements of the POPs convention.

The Editor

Residual sprays continue to play a pivotal role in the control of vector-borne diseases around the globe. They are the mainstay of malaria vector control programs in most of Africa, many countries in Asia and a good portion of the rest of the Americas. In addition, residual applications of insecticides are also employed in the control of Chagas disease vectors throughout Central and South America. Unfortunately, though this method is widely used, vector control programs frequently lack well-trained field staff that can ensure that the insecticides used are applied properly and that adequate deposition and spray patterns are obtained.

Maintaining the internal pressure of compression sprayers at the recommended operational range of between 55 to 35 psi is the first step towards achieving adequate insecticide deposition. An experienced vector control specialist knows that the internal pressure of the compression sprayer will drop as the liquid volume of the sprayer is reduced during its application on a surface.

However, even some of the most experienced specialists are surprised when provided with palpable evidence of this, see Figure 1. As the internal pressure of the sprayer drops from the recommended maximum operational level of 55psi (measuring cylinder #1) to 40psi (measuring cylinder #2) and then to 25psi (measuring cylinder #3) there is a relatively linear and uniform reduction in the output volume. However, the reduction in output volume ceases to be linear in nature when the internal pressure of the sprayer is lowered another 15psi from 25 to 10psi (see measuring cylinder #4).

The reduction in output volume resulting from a drop in the internal pressure of a compression sprayer brought about as its internal volume is depleted brings up another factor frequently overlooked: a measurable variation in the spray pattern (see Figure 2). As the sprayer pressure drops by 15psi from the highest operational pressure of 55psi (two upper band), there is a slight reduction in the effective coverage. This reduction in effective coverage continues as the pressure continues to decrease in a relatively uniform fashion and then becomes essentially useless when the sprayer's internal pressure drops below 25psi.

The last major factor influencing the effectiveness and efficacy of an indoor residual spray program is the type and condition of the nozzle used. Two types of nozzles are recommended, depending on the residual insecticide used: 8002E or 8001E. The latter one is used when insecticides other than pyrethroids are sprayed whereas the former is normally installed when residual formulations of pyrethroids are applied.

Maintaining proper nozzle orientation -see Figure 3, letter "A"- is the first step in ensuring adequate coverage and deposition. Orientation must be tested in a small corner of the surface to be sprayed to ensure that the spray is oriented correctly. Though unnoticeable to the untrained eye, the deposition pattern between an 8002 and 8002E nozzle is significantly different -see letters "B" and "D" on Figure 3. The edges of the material sprayed using an 8002 nozzle (letter "D") are diffuse as compared with those produced by the 8002E (letter "B"). Finally, the material sprayed using an 8001 nozzle is noticeably less than that sprayed using an 8002 nozzle -letter "C" and "B," respectively.

One of the factors most overlooked by many vector control programs conducting indoor residual spraying is nozzle age. A nozzle that has outlived its useful life will produce uneven deposition patterns with gaps where a sub-lethal dose of insecticide is deposited -see letter "E" on Figure 3). This produces an uneven insecticide deposition pattern and provides gaps where vectors can come to rest without coming in contact with a lethal dose of the material sprayed.

The editor would like to thank Mr. Anton Gericke of Avima in South Africa for conducting the field demonstration depicted in the series of photographs in this note.